Field of the Invention
Embodiments of the present application relate to the art of a vehicle control system including engagement mechanisms including a clutch and a brake between a prime mover and drive wheels, and particularly to the art of a vehicle control system for reducing torsional vibrations caused in the vehicle.
Discussion of the Related Art
Japanese Patent Publication No. 4356305 describes a vehicle control system for correcting input commands of an acceleration pedal operation and the like by feedback gain set on the basis of vertical behaviors of a vehicle found by a motion model of vibrations of the vehicle body in order to realize optimum vibration control of the vehicle body. Thereby, the motion model which is rapid in responsiveness for correcting a command as cause of vibrations and which dynamically models the vibrations of the vehicle body is used thereby to accurately correct the input commands. Thus, even when the input commands causing vibrations of the vehicle body are continuously made, the vibrations can be rapidly controlled without being scattered.
JP-A-2005-147238 describes a hydraulic control system in an automatic transmission which determines a switch between a drive state in which an engine rotation frequency is higher than an input rotation frequency and a driven state in which the input rotation frequency is higher than the engine rotation frequency and corrects a hydraulic pressure supplied to a frictional engagement element on the engagement side of the transmission on the basis of the determination result in order to reduce the occurrences of shift shock.
JP-A-2008-215580 describes a vehicle control device and method for increasing a command value in a stepwise manner for controlling hydraulic supply to frictional engagement elements provided in a transmission when a condition indicating a delay of the progress of gear shift (sweep condition) is established, and decreasing a command value in a stepwise manner when a predetermined time elapses in order to prevent a delay in gear shift time during power on/down shift and a gear shift shock from occurring. According to the teachings of JP-A-2008-215580, when it is determined that a power-down shift request is made, backlash elimination control is performed on the frictional engagement element on the engagement side and constant-pressure standby control is performed on the frictional engagement element on the engagement side after the backlash reduction control. The “backlash elimination control” is directed for increasing a command value for the frictional engagement element on the engagement side in a stepwise manner until a predetermined time elapses, and rapidly moving the frictional engagement element until immediately before its engagement.
JP-A-2006-46354 describes a vehicle control system for determining whether rattling is caused due to backlash elimination, and controlling an engagement force between frictional engagement elements such that when it is determined that rattling is caused, an engagement time from the released state of the frictional engagement elements to the engaged state is longer than that when it is determined that backlash rattling is not caused in order to restrict shock due to rattling.
However, a vehicle control system for correcting input commands by feedback gain set on the basis of vertical behaviors of a vehicle found by a motion model of vibrations of a vehicle body is more advantageous in vibration control than when feedback is performed after a vibration is caused, but acceleration responsiveness expected by a driver may not be met when an input command for acceleration pedal operation is changed, for example. Thus, vibration suppressing performance to suppress vibrations of the vehicle resulting from torque pulse, and acceleration response of the vehicle are required to be improved.